1) Field of the Invention
The present invention relates to a scroll compressor in an air conditioning apparatus, a refrigerating apparatus, and the like.
2) Description of the Related Art
A scroll compressor includes a fixed scroll and a revolving scroll. The fixed scroll includes a spiral wall that is vertically fixed to an end plate. The revolving scroll also includes a spiral wall, which has substantially the same shape as the wall of the fixed scroll, that is vertically fixed to another end plate. The scroll compressor is assembled in such a manner that the walls of the fixed scroll and the revolving scroll engage with each other. In this state, the revolving scroll is revolved with respect to the fixed scroll, whereby a volume of a compression chamber formed between the walls is gradually reduced to compress fluid in the compression chamber.
Some conventional scroll compressors are provided with a step portion between the spiral walls. The step portion is formed with surfaces at different levels. The surface that is closer to an inner end of the spiral (closer to a center of the spiral) is more distant from a surface of the end plate than the surface that is closer to an outer end of the spiral (closer to a fluid drawing port). An edge of the wall is formed in a shape engaging with a corresponding step portion. With such a structure, a fluid drawing capacity of a chamber on the outer end side of the spiral is increased, and pressure in a chamber on the inner end side is increased. Thus, an improved compression ratio is obtained without increasing an outer diameter of a scroll (e.g., Japanese Patent Publication No. S60-17956).
In other conventional scroll compressors, a fluid through hole (bypass hole) is provided in an end plate in a portion between a spiral wall of a fixed scroll. The fluid through hole is openable and closable. With this structure, by opening the fluid through hole as required, a compression volume in a compression chamber is reduced to lower a load on a drive source (e.g., Japanese Patent Publication No. H1-33675).
However, when the bypass hole is provided in a portion that is closer to the outer end of the spiral than the step portion, there is a problem in that a compression loss occurs due to leakage of fluid from an engaging part of the step portion and the wall. On the other hand, when the bypass hole is provided in a portion that is closer to the center of the spiral than the step portion, since compression is performed on the outer end side of the spiral, there is a problem in that excessive compression occurs before reducing a compression volume with the bypass hole. A load is applied to a drive source in an area where the excessive compression occurs.